A. Field of the Invention
The present invention relates to a polysilicon fuse used for trimming a semiconductor circuit, a manufacturing method thereof, and a semiconductor device including a polysilicon fuse.
B. Description of the Related Art
In order to adjust a resistance value and the like of a semiconductor circuit, a polysilicon fuse is used as a trimming device. The polysilicon fuse can be cut off by performing laser emission or voltage application. The cutting-off method using the voltage application has a particular advantage of being capable of performing adjustment together with a wafer test after the completion of the process.
FIG. 8 is a diagram that illustrates a main portion of a circuit of which the resistance is adjusted by a polysilicon fuse 500. In a case where the polysilicon fuse 500 is used for the adjustment of a resistance value or the like of a semiconductor circuit, a plurality of resistors, for example, resistors R51 to R54 are formed in advance, and the polysilicon fuse 500 is cut off.
FIGS. 9A and 9B are configuration diagrams of a conventional lateral-type polysilicon fuse 500. FIG. 9A is a plan view of a main portion thereof, and FIG. 9B is a cross-sectional view of the main portion taken along line X-X illustrated in FIG. 9A. A polysilicon film is formed on an insulating film 502 that is formed on a semiconductor substrate 501 and is patterned, whereby the polysilicon fuse 500 is formed. This polysilicon fuse 500 is a lateral-type fuse and is configured by left and right electrode portions 503 and 504 formed using polysilicon and a polysilicon portion 505 that serves as a melting portion. By causing a large current to flow through this polysilicon fuse 500, the polysilicon portion 505 serving as the melting portion is melted, and, when the melted polysilicon portion is solidified, a gap is formed (finely divided) between the solidified polysilicon portions, and the solidified polysilicon portions are electrically insulated from each other.
When the polysilicon portion is melted, in a case where the melted polysilicon is scattered around, there is a possibility that a peripheral circuit arranged on the periphery of the polysilicon fuse 500 and a device configured thereby may be damaged.
In order to suppress the scattering of polysilicon, it is preferable that a voltage applied to the polysilicon fuse 500 be low. When the applied voltage is high, the melted polysilicon is scattered much more due to a large arc current at the time of cutting off the polysilicon fuse. On the other hand, when the applied voltage is low, the melted polysilicon is scattered less, but a case may occur in which the melted polysilicon is not melted down. Next, a method for stably cutting off the polysilicon fuse even in a case where the applied voltage is low will be described.
In Japanese Patent Application Laid-Open (JP-A) No. 2004-335608, it is disclosed that a resistance value of the polysilicon portion is partially changed, and a place at which the fuse is melted is limited for stably cutting off a polysilicon fuse.
In JP-A No. 2006-41257, it is disclosed that a cavity is formed near a polysilicon fuse, and, when the polysilicon fuse is cut off, scattered polysilicon is absorbed in the cavity.
In JP-A No. 2012-39046, it is disclosed that a contact hole formed in an interlayer insulating film is used as a via-cutting-type electrical fuse. This via-cutting-type electrical fuse is a vertical-type fuse and is formed using a copper wire.
In JP-A No. 2007-305693, it is disclosed that an upper layer metal wiring and a lower layer metal wiring are connected by filling a metal member having copper as its main composition in a via formed in an interlayer insulating film, and the metal member filled in the via is used as a vertical-type fuse.
However, the polysilicon fuse 500 illustrated in FIGS. 9A and 9B and the polysilicon fuses illustrated in JP-A Nos. 2004-335608 and 2006-41257 are lateral-type fuses allowing a current to flow in the lateral direction, and accordingly, the occupied areas thereof are large.
In addition, in a case where a circuit element is arranged near the polysilicon fuse 500 so as to decrease chip size, cutting-off is performed with a low in order to decrease the scattering of melted polysilicon.
When the polysilicon fuse 500 is melted down with a low voltage, polysilicon is finely divided to be in an insulated state. However, there are cases where the polysilicon, which has been finely divided to be in the insulated state, is connected together during actual operation of the semiconductor device so as to form a leakage path, and defective insulation occurs. As a result, there is a problem that a characteristic value of the semiconductor device changes.
In addition, the above-described fuses disclosed in JP-A Nos. 2012-39046 and 2007-305693 are formed using metal, and there is no description of a polysilicon fuse. An object of the present invention is to solve the above-described problems and to provide a polysilicon fuse capable of securing good insulation after being cut into small areas, a manufacturing method thereof, and a small-size and highly-reliable semiconductor device including a polysilicon fuse.